May 31, 2020

Review: How to Build a Habitable Planet by James Kasting.

Some years ago, a book entitled Rare Earth was published amid much controversy. The central thesis of this work was that events that led to the eventual habitability and diversity of life and intelligence on Earth were so improbable, as be near to impossible to replicate elsewhere in our galaxy. The book marked a sort of change in thinking in the realm of exobiology, one from “intelligent civilizations are everywhere” championed by the late Carl Sagan to the concept that we may be the only ones, if not the first.

As the science fiction writer Arthur C. Clarke once said, either idea has stunning consequences…

Now, another such shift in thinking is underway again. This is heralded by the book How to Build a Habitable Planet by James Kasting and out by Princeton Press. Mr. Kasting is a  considerable authority on the subject. A Distinguished Professor of Geosciences at Pennsylvania State University, he is actively involved with NASA in the search for Earth-like worlds.  The book pulls together all of the latest research to paint a picture of how our planet formed and became a stable haven for life as we know it. Kasting serves up the examples of our nearest planetary neighbors skirting the habitable zone of our solar system, as Mars and Venus get a chapter each. We’ve always thought that it was fortuitous that we have two good studies in comparative planetary science in our solar system. Venus, about the size of the Earth, shows us how things might be without liquid water closer in to the Sun, and Mars shows us how life would be at a tinier size and without a magnetic field. The author also tackles the “faint sun paradox;” It is known that the Sun was appreciably dimmer earlier in its history; how then, did we avoid a scenario of a “snowball Earth?” The author backs up the discussion with hard data throughout. Other puzzles are tackled, such as the source of the Earth’s oceans and the secret life of methagens in the early history of life on our planet.

The author also takes the dilemma of the Rare Earth Hypothesis head-on and intelligently addresses the pros and cons of the issue. The author is wise to point out that it is simply too early in our search to definitively shout out “We are alone!” Right now, we can only base this conclusion on a biosphere sample of one; discovery of even ancient microbial life elsewhere in our own solar system would have immense repercussions for the search for life elsewhere, as well as narrow in on a key parameter of the Drake Equation…

And speaking of which, the author devotes the last half of the book to the search for extra-solar planets. Currently the hottest field in astronomy today, discoveries are coming in at a fast and furious rate. The refinement in techniques and technologies are leading up to a tantalizing goal; the imaging of an Earth-like world. If a spectrum can be obtained, key signatures could be ferreted out. Markers such as methane, water vapor, and free O2 and O3 may be clues that something biologically interesting is taking place on a far off world. The author covers current search methods of radial spectroscopy and catching exoplanet transits and touches on the future promises of such missions as the Kepler Space Telescope, ESAs Gaia, and the Terrestrial Planet Finder series. Farther on down the road, the author envisions such intriguing concepts as the Exo-Earth Detector, a constellation of free flying telescopes that could form one giant hyper-telescope. Other mind-bending ideas include placing a telescope at a distance of 600 A.U. and using our own Sun as a giant gravitational lens. Or how about actually targeting an exo-Earth in our galactic neighborhood with a probe propelled by a solar sail driven by a Moon- or space-based laser? The author points out that such a device was depicted in Larry Niven’s The Mote in God’s Eye, and would have the advantage of not having to carry its own inertia-filled fuel…

Read How to Build a Habitable Planet to get a fascinating look at our evolving understanding of how our Earth came to be, and our efforts to define our place in the cosmos. We may not be rare, but the Earth from our vantage point is truly a special place, and our home. And one day we hope to have background of an Exo-Earth adorning our laptop!



  1. [...] Review: How to Build a Habitable Planet by James Kasting. : Astro Guyz [...]

  2. [...] the science behind solar system formation. It would make a great companion read to James Kasting’s How to Build a Habitable Planet or an updated answer to the landmark book Rare Earth published in 2000. How typical is the tale of [...]

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